1. Field of the Invention
This invention relates to the stabilization with respect to electromagnetic radiation of organic compounds, particularly to the stabilization of dyes used in photographic applications, especially those used in photographic elements.
2. Description of the Prior Art
A need has been long recognized in the photographic arts for imaging dyes which are more resistant to fading upon extended exposure to electromagnetic radiation, such as ambient light. It is common practice to form color photographic images using combinations of dyes which form subtractive primary colors. Such subtractive primary dyes are those which absorb light predominantly in one of the blue, green and red triads of the visible spectrum thereby appearing yellow, magenta or cyan, respectively. In the most common arrangement these subtractive primary dyes lie in separate layers of the photographic element. In such photographic elements the magenta dyes have shown a particular propensity toward fading upon prolonged exposure to light.
One approach toward solving the disadvantages of dye fading in photographic elements has been to devise dyes of improved stability. Lestina U.S. Pat. No. 3,519,429, issued July 7, 1970, and Weissberger et al U.S. Pat. No. 3,062,653, issued Nov. 6, 1962, are illustrative of patents teaching the formation of stabilized magenta dyes through the formation of novel magenta-dye-forming couplers.
Another approach to solving the disadvantage of dye fading in photographic elements has been to reduce the amount of ultraviolet light contacting the imaging dyes. This can be accomplished by providing the photographic element with an ultraviolet light filter as an overcoat to the dye image-forming layers.
It is also known to place stabilizing compounds in combination with imaging dyes directly within the image-forming layers of photographic elements. Such stabilizers are capable of protecting the imaging dyes to some extent against fading in response to extended exposure to visible and ultraviolet light. These stabilizers are characterized by fused heterocyclic ring systems and are typically phenolic type compounds. Exemplary stabilizers of this type are disclosed in Lestina et al U.S. Pat. Nos. 3,432,300; 3,573,050 and 3,698,909, issued Mar. 11, 1969; Mar. 30, 1971; and Oct. 17, 1972, respectively.
It is known to form dye images in photographic elements by placing in a single imaging layer combinations of couplers capable of forming imaging dyes upon development. One very common illustration of such photographic elements are those which incorporate into a photographic imaging layer a combination of colored and uncolored couplers. The colored couplers have as their purpose to minimize the imagewise formation of unwanted color in photographic negatives resulting from light absorption by the dye formed from the uncolored coupler outside of the desired absorption triad of the visible spectrum. Illustrative of patents which teach the combination of couplers which are colored and uncolored for the purpose of masking unwanted dye absorption are Vittum et al U.S. Pat. No. 2,428,054, issued Sept. 30, 1947; Whitmore U.S. Pat. No. 2,808,329, issued Oct. 1, 1957; Jaeken et al U.S. Pat. Nos. 3,525,614 and 3,535,113, issued Aug. 25, 1970 and Oct. 20, 1970, respectively; Oishi et al U.S. Pat. No. 3,642,485, issued Feb. 15, 1972; Guzzi et al U.S. Pat. No. 3,647,468, issued Mar. 7, 1972 and Otto et al U.S. Pat. No. 3,671,257, issued June 20, 1972.
It also known in the art to incorporate into a single imaging layer of a photographic element imaging dyes which absorb predominantly in different triads of the visible spectrum. Bodmer et al U.S. Pat. No. 3,265,503, issued Aug 9, 1966 and White U.S. Pat. No. 2,350,380, issued June 6, 1944, teach placing yellow and magenta dye-forming couplers in a single imaging layer of a photographic element. Friedman U.S. Pat. No. 2,689,180, issued Sept. 14, 1954, teaches forming gray dye images by placing a mixture of yellow, magenta and cyan-dye-forming couplers in a single imaging layer of a photographic element. Barr et al U.S. Pat. No. 3,277,554, issued Jan. 4, 1966, teaches placing magenta and yellow as well as cyan and yellow-dye-forming couplers in a single layer of a photographic element. Barr et al also teaches placing within a single layer of a photographic element couplers intended to form imaging dyes and couplers intended to release development modifying moieties, such as mercaptans.
Since infrared radiation is not visible to the human eye, this portion of the spectrum is usually ignored or assigned little importance in constructing photographic elements capable of producing dye images. Generally the infrared portion of the electromagnetic spectrum has been usefully employed only for specialized photographic applications. Woodward et al U.S. Pat. No. 2,927,024, issued March 1, 1960, places a combination of yellow and magenta-dye-forming couplers in an infrared sensitized silver halide emulsion layer for the purpose of masking unwanted absorption by the imaging dyes in the imaging layer of the photographic element. In German Pat. No. 2,302,661, a color photographic element is disclosed formed of three separate subtractive primary dye-forming imaging layers. For the purpose of forming an integral sound track in the photographic element which will provide adequate density when scanned with an infrared radiation source, it is taught to incorporate an infrared absorbing dye-forming coupler. The coupler can be incorporated in the red-sensitized layer of the photographic element to serve as the cyan dye-forming coupler as well as providing its infrared absorbing function or can be placed in the red-sensitized layer of the photographic element in combination with a conventional cyan dye-forming coupler.